Powder injection mold assembly and method of molding

ABSTRACT

A mold assembly for powder injection molding of a shaped element includes a first mold portion having a first surface defining a first portion of the mold cavity and releasably engageable to the feedstock and a second mold portion having a second surface defining a second portion of the mold cavity and releasably engageable to the feedstock. The first mold portion has a first thermal capacity and a first thermal conductivity, and the second mold portion has a second thermal capacity and a second thermal conductivity. At least one of the first thermal capacity and the first thermal conductivity is lower than a respective one of the second thermal capacity and the second thermal conductivity and/or than a respective one of the thermal conductivity and thermal capacity of solid metal. A method of molding a green part is also discussed.

TECHNICAL FIELD

The application relates generally to powder injection mold assemblies, and more particularly to metal injection molding mold assemblies and method for molding a metal element

BACKGROUND OF THE ART

In powder injection molding (PIM), the solidification of the feedstock can be achieved by relying on the heat transferred to the cooler mold, or by heating the mold during injection and then cooling it to solidify the part. In either case, there are many challenges in creating complex passages and thin walls inside of a molded part. As the feedstock cools, its viscosity increases until it finally solidifies. Frequent changes in velocity, direction, and/or cross-sectional area of the passages tend to increase the heat loss, thus reduce the time before the feedstock solidifies, which can create injections defects. Flow lines, trapped air, and/or incomplete filling of the mold can occur during cooling/solidification and can cause defects in the shaped element. For example, if the shaped element includes adjacent holes, very thin material portion between the holes can remains unfilled as, during injection, the feedstock rapidity solidifies in the thin cavity portion of the mold assembly due to the high thermal capacity and conductivity of the mold material.

Heating the mold to prevent defects in the shaped element greatly increases the energy and cost necessary to perform the PIM process, and affects the time required for injection because of the difficulties in attaining a steady state. In addition, careful control of heat transfer during filling and solidification of the feedstock is required in PIM.

SUMMARY

In one aspect, there is provided a mold assembly for powder injection molding of a shaped element, the mold assembly defining a mold cavity for receiving a feedstock and comprising: a first mold portion having a first surface defining a first portion of the mold cavity and releasably engageable to the feedstock, the first mold portion having a first thermal capacity and a first thermal conductivity; and a second mold portion having a second surface defining a second portion of the mold cavity and releasably engageable to the feedstock, the second mold portion having a second thermal capacity and a second thermal conductivity; wherein at least one of the first thermal capacity and the first thermal conductivity is lower than a respective one of the second thermal capacity and the second thermal conductivity.

In another aspect, there is provided a mold assembly for powder injection molding of a shaped element, the mold assembly comprising: a first mold part and a second mold part cooperating to define a mold cavity, the first mold part and the second mold part being movable relative to one another to selectively open and close the mold cavity, the first and second mold parts being disengageable from the shaped element after molding; the first mold part comprising an integral mold portion having a surface defining the mold cavity, the mold portion made of a material different from solid metal and having at least one of a thermal capacity and a thermal conductivity lower than that of solid metal.

In a further aspect, there is provided a method of molding a green part, the method comprising: injecting a powder injection molding feedstock in a mold cavity defined in a mold assembly; extracting heat from the feedstock in the mold cavity through a first portion of the mold having a first surface in contact with the feedstock and through a second portion of the mold having a second surface in contact with the feedstock, a first heat flux through the first surface and first portion being lower than a second heat flux through the second surface and second portion to allow the feedstock to fill the mold cavity before solidification; solidifying the feedstock to create the green part; and disengaging the green part from the first and second portions of the mold by extracting the green part from the mold cavity.

DESCRIPTION OF THE DRAWINGS

Reference is now made to the accompanying figures in which:

FIG. 1a is a schematic cross-sectional view of a mold assembly in accordance with a particular embodiment;

FIG. 1b is a schematic cross-sectional view of a mold assembly in accordance with another particular embodiment;

FIG. 2a is a schematic cross-sectional view of a mold assembly in accordance with another particular embodiment, with hollow metal pins;

FIG. 2b is a schematic cross-sectional view of a hollow metal pin of the mold assembly of FIG. 2 a;

FIG. 3a is a schematic cross-sectional view of a mold assembly in accordance with another particular embodiment, with pins integral to one mold part;

FIG. 3b is a schematic cross-sectional view of the mold assembly of FIG. 3a , taken along line B-B;

FIG. 3c is a schematic cross-sectional view of a mold assembly in accordance with another particular embodiment, with pins integral to two mold parts;

FIG. 4a is a schematic cross-sectional view of a mold assembly in accordance with another particular embodiment; and

FIG. 4b is a schematic cross-sectional view of a mold assembly in accordance with another particular embodiment.

DETAILED DESCRIPTION

Referring to FIGS. 1a to 4b , there is provided various mold assemblies 10, 10′, 110, 210, 210′, 310, 310′ (hereinafter, mold assemblies 10-310′) used in a powder injection molding (PIM) process for producing a shaped element. In a particular embodiment, mold assemblies 10-310′ can be used in metal injection molding (MIM) to mold a green part used to produce a metal element.

In a PIM process a feedstock comprising a material powder and a binder is injected in a mold assembly. Examples of possible powder materials include high temperature resistant powder metal alloys, such as a cobalt alloy or nickel-based superalloy, or ceramic, glass, carbide or composite powders or mixtures thereof. In MIM processes the powder material is a metal powder. Other high temperature resistant material powders which may include one material or a mix of materials could be used as well.

The binder can include one or more binding material(s). The binder can include various components such as surfactants which are known to assist the injection of the feedstock into the mold assembly for production of the shaped element. In a particular embodiment, the binder includes a mixture of binding materials, for example including a lower melting temperature polymer, such as a polymer having a melting temperature below 100° C. (e.g. paraffin wax, polyethylene glycol, microcrystalline wax) and a higher melting temperature polymer or polymers, such as a polymer or polymers having a melting temperature above 100° C. (e.g. polypropylene, polyethylene, polystyrene, polyvinyl chloride). Other suitable materials or mix of materials could be used as well.

In a particular embodiment, the solid loading of the feedstock (i.e. the proportion of binder/powder material) is of 60%, or of more than 60%, where the solid loading is determined on a volume basis as VP/(VP+VB) wherein VP is the volume of powder material and VB the volume of binder. In a particular embodiment, the solid loading is selected to facilitate heat transfer within the feedstock so as to facilitate cooling and solidifying of the portions of the part not in direct contact with the surfaces of the mold assembly.

Powder injection molding can be performed under low or high pressure conditions. In a particular embodiment, the PIM process is performed at a pressure range of less than 100 psi, preferably in a range of 50 to 100 psi. Lower pressures allow using mold portions of lower strength, such as hollow metal portions or plastic portions coated with metal.

Mold assemblies 10-310′ can be used for molding green parts for obtaining metal elements, such as gas turbine engine components for aircraft. In a particular embodiment, the metal element to be produced, and accordingly the corresponding molded green part, has at least one portion that has low thickness or complex geometry. For example the metal element can be a gas turbine engine component having a plurality of adjacent holes therein, the holes forming a complex network of channels in the mold cavity, where the flow of the feedstock may be difficult. The metal element can also comprise thin portions, molded with corresponding thin portions of the mold cavity, where the flow of the feedstock may also be difficult. In a particular embodiment, the metal element is a heat shield panel including a plate having a small thickness, for example about 0.036 inch. In another embodiment, the metal element is a swirler for a fuel nozzle, including a plurality of differently angled holes, with a thickness of material between adjacent holes being small, for example 0.010 inch or less. Other types of elements are also possible.

The mold assemblies 10-310′ are used to mold the shaped element as a green part. The green part, once separated from the mold assembly 10-310′, is then debound to produce a brown part, then sintered to produce the final element.

Referring to FIG. 1a , a mold assembly 10 in accordance with a particular embodiment is shown. The mold assembly 10 defines a mold cavity 12 for receiving the feedstock therein. It is understood that the configuration shown for the mold assembly 10 is exemplary only, and that the mold cavity 12 has a shape substantially corresponding to the shape of the shaped element to be molded.

In a particular embodiment shown in FIG. 1a , the mold assembly 10 comprises a first mold part 14 and a second mold part 16. The first mold part 14 and the second mold part 16 are movable relative to one another to selectively open and close the mold cavity 12. In a closed configuration the first mold part 14 and the second mold part 16 are engaged and secured to receive and retain the feedstock in the mold cavity 12. It is understood that the mold assembly 10 can comprise more than two mold parts movable relative to one another and engageable to close the cavity.

The first mold part 14 and the second mold part 16 are disengageable from the shaped element after molding. Once the feedstock is molded (i.e. the feedstock is cooled until the binder has reached a solid state), the first mold part 14 and the second mold part 16 are disengaged from one another and from the shaped element. Therefore, the shaped element is removed from the mold assembly 10 when it is in an open configuration and none of the first mold part 14 or second mold part the 16 remains engaged with the shaped element.

The mold assembly 10 includes a first mold portion 18 and a second mold portion 20 which have different thermal capacities and/or different thermal conductivities from each other. Each portion can be defined by a respective one of the mold parts 14, 16, or both portions can be defined in a same one of the mold parts 14, 16. In FIG. 1a , the first mold portion 18 is an integral portion of the first mold part 14, and the second portion 20 is defined by a remainder of the first mold part 14 and by the second mold part 16.

The first mold portion 18 has a first surface 22 defining a first portion 24 of the mold cavity 12. The second mold portion 20 has a second surface 26 defining a second portion 28 of the mold cavity 12. The first and second surfaces 22, 26, are in contact with the feedstock when the feedstock is injected and flows in the mold cavity 12 so that heat can be transferred from the feedstock to the first and second mold portions 18, 20 through the first and second surface 22, 26, respectively.

The first mold portion 18 and second mold portion 20 are integral elements of the mold assembly 10 and releasably engageable to the feedstock. Therefore, the first surface 22 and the second surface 26 enter in contact with and engage the feedstock when the feedstock flows in the mold cavity 12. Heat is then removed through the first surface 22 and through the second surface 26 and the feedstock solidifies. However, when the shaped element is removed from the mold assembly 10, the first portion 18 and the second portion 20 are disengaged from the shaped element.

The first mold portion 18 has a first thermal capacity and a first thermal conductivity. The second mold portion 20 has a second thermal capacity and a second thermal conductivity. In a particular embodiment, the first thermal capacity is lower than the second thermal capacity and/or the first thermal conductivity is lower than the second thermal conductivity. As used herein, “thermal capacity” refers to the ratio of heat added/removed from an object to the resulting temperature change, i.e. the ability of a material to absorb heat, while “thermal conductivity” refers to the rate at which heat flows through a material, i.e. the ability of a material to transfer heat therethrough; accordingly, a lower thermal capacity results in a material having a lower ability to absorb heat, and a lower thermal conductivity results in a material having a lower ability to transfer heat therethrough, both of which resulting in a lower quantity of heat being removed from a component (e.g. feedstock) adjacent to that material in a given period of time. Therefore, the flux of heat through the first surface 22 and first portion 18 is lower than the flux of heat through the second surface 26 and second portion 20 so that a smaller amount of heat is removed from the feedstock in the first portion 24 of the mold cavity 12 than from the feedstock in the second portion 28 of the mold cavity 12.

In a particular embodiment, the first mold portion 18 having the lower thermal capacity and/or thermal conductivity is made of a material different from solid metal. Therefore, the first mold portion 18 has a thermal capacity that is lower than the thermal capacity of solid metal and/or a thermal conductivity that is lower than the thermal conductivity of solid metal. The thermal capacity and thermal conductivity of the first mold portion 18 can both be lower than that of solid metal, or only one of the thermal capacity and conductivity can be lower than that of solid metal. As a consequence, the heat flux through the first surface 22 and first portion 18 is lower than through a similar portion made of solid metal material.

In the embodiment shown in FIG. 1a , the first and second mold portions 18, 20 are made of solid material, with the solid material of the first mold portion 18 having a lower thermal capacity and thermal conductivity than the solid material of the second mold portion 20. For example, the first mold portion 18 can be made of plastic, ceramic, glass or a combination thereof while the second mold portion 20 is made of metal. Other combinations of materials are also possible. In a particular embodiment the thermal conductivity of the first mold portion 18 is in the range of 0.1 to 0.5 W/mK while the thermal conductivity of the second mold portion 20 is in the range of 10 to 60 W/mK. Other values are also possible.

Referring to FIG. 1b , a mold assembly 10′ in accordance with another particular embodiment is shown, where elements similar to that of the mold assembly 10 are referred to using the same reference numeral and will not be described further herein. The mold assembly 10′ differs from the mold assembly 10 of FIG. 1a in that first mold portion 18′ includes a core 30 coated with a layer 32 defining the surface 22 of the mold cavity 12, the core 30 and layer 32 being made of different materials. One of the core 30 and the layer 32 may be made of the same material as the second mold portion 20. Alternately, both the core 30 and layer 32 may be made of a different material than that of the second mold portion 20.

In a particular embodiment, the core 30 is made of metal, and the layer 32 is made of plastic, ceramic or glass. In that case, the layer 32 has a lower conductivity than solid metal and insulates the metal core 30 so that the heat flux through the first surface 22 and first portion 18′ is reduced with respect to that through the second surface 26 and second portion 20.

In another embodiment, the core 30 is made of plastic, ceramic or glass, and the layer 32 is made of metal, so as to allow a polished finish of the molded surface, have increased wear, and/or reduce chemical interactions between the core 30 and the feedstock; other advantages could also motivate the use of a layer 32 of different material. The presence of the core 30 allows for the first portion 18′ to have a lower total thermal capacity than a first portion 18′ completely made of solid metal, so that the heat flux through the first surface 22 and first portion 18′ is lower than through the second surface 26 and second portion 20.

Alternately, the core 30 may be replaced by an insulating cavity filled with air or with any other suitable gas, so that the first mold portion 18′ is configured as a thermal insulating storage container. As air is a good thermal insulator, the flux of heat through the first surface 22 and first portion 18′ is reduced compared to a solid mold portion made of the same material as that of the layer 32.

Referring to FIGS. 2a and 2b , a mold assembly 110 in accordance with another particular embodiment is shown, which also includes first and second mold parts 114, 116 movable relative to one another to selectively open and close the mold cavity 112, and disengageable from the shaped element after molding. The mold assembly 110 also includes a first mold portion 118 and a second mold portion 120 which have different thermal capacities and/or different thermal conductivities from each other.

In this embodiment, the first mold portion 118 is integral to the first mold part 114 and the second mold portion 120 includes the remainder of the first mold part 114 and an entirety of the second mold part 116. The first mold portion 118 defines a plurality of pins, protruding within the mold cavity 112 to allow formation of holes in the shaped element. The first mold portion 118 defines a first portion 224 of the mold cavity 112 that has a cross-section that is smaller than the cross-section of a second portion 228 of the mold cavity 112 which is defined by the second mold portion 120. In a particular embodiment, a smaller cross-section causes change in the direction and/or velocity of the flow of feedstock injected and flowing in the mold cavity 112. As shown in FIG. 3b , the pins 118 can define a network 246 within the mold cavity 212, in which the direction and/or the velocity of the feedstock flowing in the mold cavity 212 changes.

Referring back to FIG. 2b , each pin includes a layer 138 of material, for example a metal layer, defining the first surface 122 in contact with the feedstock, and having an inner surface 140 opposed to the first surface 122; the inner surface 140 defines an insulating cavity 142. The presence of the insulating cavity 142 reduces the total thermal capacity of the pins defining the first mold portion 118, which in a particular embodiment slows the cooling of the feedstock in the associated portion 224 of the mold cavity 112, thus improving the flow in the restricted areas of the mold cavity 112.

Alternately, the insulating cavity 142 may be replaced by a core made of a different material than that of the layer 138, where the core or the layer 138 may be made of the same material as the second mold portion 120. As previously mentioned, various combinations are possible, including, but not limited to, a metal core with a plastic, ceramic or glass layer, and a plastic, ceramic or glass core with a metal layer.

Referring to FIG. 3a , a mold assembly 210 in accordance with another particular embodiment is shown, where elements similar to that of the mold assembly 110 are referred to using the same reference numeral and will not be described further herein. Similarly to the mold assembly 110, the first mold portion 218 includes a plurality of pins. In this embodiment however, the first mold portion 218 is made of a solid material different than that of the second mold portion 120. For example, the first mold portion 218 can be made of plastic, ceramic, glass or a combination thereof while the second mold portion 120 is made of metal. Other combinations of material are also possible.

Referring to FIG. 3c , a mold assembly 210′ in accordance with another particular embodiment is shown, where elements similar to that of the mold assembly 210 are referred to using the same reference numeral and will not be described further herein. Similarly to the mold assembly 110, 210, the first mold portion 218′ includes a plurality of pins. In this embodiment however, the first mold portion 218′ is integral to both the first mold part 114 and the second mold part 116, i.e. some of the pins are an integral part of the first mold part 114 while some of the pins are an integral part of the second mold part 116. Although the first mold portion 218′ is depicted as being made of solid material, it is understood that alternately, it can include insulating cavities such as in the first mold portion 118 of FIGS. 2a-2b , or a core surrounded by a layer defining the surface of the mold cavity in contact with the feedstock.

Referring to FIG. 4a , a mold assembly 310 in accordance with another particular embodiment is shown, which also includes first and second mold parts 314, 316 movable relative to one another to selectively open and close the mold cavity 312, and disengageable from the shaped element after molding. The mold assembly 310 also includes a first mold portion 318 and a second mold portion 320 which have different thermal capacities and/or different thermal conductivities from each other.

In this embodiment, the first mold portion 318 correspond to the first mold part 314 and the second mold portion 320 corresponds to the second mold part 316; the two mold parts 314, 316 as a whole thus have different thermal capacities and/or different thermal conductivities from each other. Alternate configurations are also possible.

The first surface 322 of the first mold portion 318 and the second surface 326 of the second mold portion 320 are in proximity to each other when the mold assembly 310 is closed, so as to define a mold cavity 312 having a small thickness, defining for example a plate or sheet like shaped element, for example a platform of a metal heat-shield panel used in gas turbine engine. In this embodiment, the first mold portion 318 is made of solid material having a lower thermal capacity and thermal conductivity than the material of the second mold portion 320 and/or than that of solid metal. For example, the first mold portion 318 can be made of plastic, ceramic, glass or a combination thereof while the second mold portion 320 is made of metal. Other combinations of materials are also possible.

Referring to FIG. 4b , a mold assembly 310′ in accordance with another particular embodiment is shown, where elements similar to that of the mold assembly 310 are referred to using the same reference numeral and will not be described further herein. The mold assembly 310′ differs from the mold assembly 310 in that the first mold portion 318′ includes a core 330 coated by an outer layer 332 defining the surface 322 in contact with the feedstock, with the core 330 and layer 332 being made of different materials, and where the core 330 or the layer 332 may be made of the same material as the second mold portion 320. In a particular embodiment, the core 330 is made of metal, and the layer 332 is made of plastic, ceramic or glass. In another embodiment, the core 330 is made of plastic, ceramic or glass, and the layer 332 is made of metal, so as to allow a polished finish of the molded surface, have increased wear, and/or reduce chemical interactions between the core 330 and the feedstock; other advantages could also motivate the use of a layer 332 of different material.

It is understood that although the first mold portion 18, 18′, 118, 218, 318, 318′ is depicted in the Figures as being an element of an upper mold part of the assembly, it is understood that the mold assembly 10-310′ can have any other suitable orientation.

In a particular embodiment, mold assemblies 10-310′ using mold portions having a conductivity and/or a thermal capacity lower than that of solid metal and/or lower than that of another mold portion of the mold assembly 10-310′ allow complete filling of the mold cavity, elimination of weld lines and/or elimination of air entrapment, by effectively slowing the cooling and thus slowing the increase in viscosity and the subsequent solidification of the feedstock, thus facilitating flow of the feedstock in restricted regions of the mold cavity.

In use in a particular embodiment, a shaped element is molded using powder injection molding, for example metal injection molding, in accordance with the following. The feedstock having a composition and a solid loading as defined above is injected in the mold cavity defined in the mold assembly 10-310′. The feedstock is injected as a viscous suspension to be solidified by extracting heat through the mold assembly 10-310′. Heat is extracted from the feedstock through the first mold portion 18, 18′, 118, 218, 218′, 318, 318′ having a first surface contacting the feedstock, and through a second mold portion 20, 120, 320 having a second surface contacting the feedstock. The first surface defines a first portion of the mold cavity and the second surface defines a second portion of the mold cavity.

In a particular embodiment, the heat flux through the first surface and first mold portion 18, 18′, 118, 218, 218′, 318, 318′ is lower than the heat flux through the second surface and second mold portion 20, 120, 320, so as to slow the increase in viscosity and the subsequent solidification of the feedstock in the first portion of the mold cavity as compared to what it would be if the two portions were made of material having the same thermal properties. The feedstock can therefore fill the entire mold cavity before solidifying, thereby preventing formation of flow lines, weld lines, trapping of air or other defects in the shaped element. This can also decrease the pressure required to fill the mold cavity and further decrease the number of possible defects.

The first mold portion 18, 18′, 118, 218, 218′, 318, 318′ is made of a material having a first thermal capacity and a first thermal conductivity. The second mold portion 20, 120, 320 is made of a material having a second thermal capacity and a second thermal conductivity. In a particular embodiment, at least one of the first thermal capacity and the first thermal conductivity is lower than a respective one of the second thermal capacity and second thermal conductivity, and/or at least one of the first thermal capacity and the first thermal conductivity is lower than that of solid metal.

Once the feedstock is solidified to create the green part, the green part is disengaged from the mold portions 18, 18′, 118, 218, 218′, 318, 318′, 20, 120, 320 by extracting the green part from the mold cavity. The green part can then be debound and sintered to create the metal element.

The above description is meant to be exemplary only, and one skilled in the art will recognize that changes may be made to the embodiments described without departing from the scope of the invention disclosed. Modifications which fall within the scope of the present invention will be apparent to those skilled in the art, in light of a review of this disclosure, and such modifications are intended to fall within the appended claims. 

1. A mold assembly for powder injection molding of a shaped element, the mold assembly defining a mold cavity for receiving a feedstock and comprising: a first mold portion having a first surface defining a first portion of the mold cavity and releasably engageable to the feedstock, the first mold portion having a first thermal capacity and a first thermal conductivity; and a second mold portion having a second surface defining a second portion of the mold cavity and releasably engageable to the feedstock, the second mold portion having a second thermal capacity and a second thermal conductivity; wherein at least one of the first thermal capacity and the first thermal conductivity is lower than a respective one of the second thermal capacity and the second thermal conductivity.
 2. The mold assembly according to claim 1, wherein the first mold portion comprises a plurality of pins protruding within the mold cavity for defining holes in the shaped element, and wherein the first portion of the mold cavity adjacent the pins has a cross-section smaller than a cross-section of the second portion of the mold cavity.
 3. The mold assembly according to claim 2, wherein the pins are hollow metal pins.
 4. The mold assembly according to claim 1, wherein the first mold portion includes a core coated by a layer defining the first surface, the core and layer being made of different materials.
 5. The mold assembly as defined in claim 4, wherein the core and the second mold portion are made of the same material.
 6. The mold assembly as defined in claim 4, wherein the layer and the second mold portion are made of the same material.
 7. The mold assembly as defined in claim 1, wherein the first mold portion is at least partially made of plastic, ceramic, glass or a combination thereof.
 8. The mold assembly according to claim 1, wherein the first thermal conductivity is within a range of 0.1 to 0.5 W/mK.
 9. The mold assembly according to claim 1, wherein the first mold portion includes a layer defining the first surface and having an internal surface opposed to the first surface, the internal surface defining an insulating cavity.
 10. A mold assembly for powder injection molding of a shaped element, the mold assembly comprising: a first mold part and a second mold part cooperating to define a mold cavity, the first mold part and the second mold part being movable relative to one another to selectively open and close the mold cavity, the first and second mold parts being disengageable from the shaped element after molding; the first mold part comprising an integral mold portion having a surface defining the mold cavity, the mold portion made of a material different from solid metal and having at least one of a thermal capacity and a thermal conductivity lower than that of solid metal.
 11. The mold assembly according to claim 10, wherein the mold portion comprises a plurality of pins protruding within the mold cavity for defining holes in the shaped element, and wherein a portion of the mold cavity adjacent the pins has a cross-section smaller than a cross-section of an adjacent portion of the mold cavity.
 12. The mold assembly according to claim 11, wherein the pins are hollow metal pins.
 13. The mold assembly according to claim 10, wherein the mold portion includes a core coated by a layer forming the surface defining the mold cavity, the core and layer being made of different materials.
 14. The mold assembly according to claim 10, wherein the core is made of plastic, ceramic or glass and the layer is a metal layer.
 15. The mold assembly according to claim 10, wherein the core is made of metal and the layer is a plastic, ceramic or glass layer.
 16. The mold assembly according to claim 10, wherein the thermal conductivity of the mold portion is within a range of 0.1 to 0.5 W/mK.
 17. The mold assembly according to claim 10, wherein the mold portion includes a layer forming the surface defining the mold cavity and having an opposed internal surface, the internal surface defining an insulating cavity.
 18. A method of molding a green part, the method comprising: injecting a powder injection molding feedstock in a mold cavity defined in a mold assembly; extracting heat from the feedstock in the mold cavity through a first portion of the mold having a first surface in contact with the feedstock and through a second portion of the mold having a second surface in contact with the feedstock, a first heat flux through the first surface and first portion being lower than a second heat flux through the second surface and second portion to allow the feedstock to fill the mold cavity before solidification; solidifying the feedstock to create the green part; and disengaging the green part from the first and second portions of the mold by extracting the green part from the mold cavity.
 19. The method according to claim 18, wherein extracting heat from the feedstock comprises providing the first portion with a first thermal capacity lower than a second thermal capacity of the second portion.
 20. The method according to claim 18, wherein extracting heat from the feedstock comprises providing the first portion with a first thermal conductivity lower than a second thermal conductivity of the second portion. 